Blends of ester lubricants



3,309,318 BLEND?) F EEETZJR LUBRICANTS Robert D. Ayiesworth and Raymond H. Boehringer, Cincinnati, Qrhio, assignors to Emery indnstries, inn, Cincinnati, Gino, a corporation of Ghio No Drawing. Fiied Apr. 30, 1965, er. No. 452,377 Claims. (Cl. 25256) This invention relates to synthetic lubricant compositions, particularly synthetic lubricants suitable for use in gas turbine engines.

Aircraft gas turbine engines are becoming increasingly difficult to lubricate because operating temperature has been steadily increasing. With the increase in operating temperature, demands on functional properties such as oxidation stability and corrosion resistance have become more severe. Lubricants designed to operate at these higher temperatures (e.g., up to 425 F.) have been prepared using as base fluids esters of hindered polyols with monocarboxylic alkanoic acids. Such esters are formed by reacting hindered polyols, such as neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol and dipentaerythrito-l with one or more monobasic alkanoic acids containing 5 to carbon atoms. Hindered polyols are polyhydroxy compounds having at least two methylol groups bonded to a tertiary carbon atom. Esters made from these hindered polyols exhibit excellent resistance toward oxidation and corrosion under the relatively severe conditions encountered at the operating temperatures of jet engines.

A major shortcoming of these hindered esters, however, is the inability to have functional viscosity properties at low temperatures, such as -65 F. The US. Air Force specifies that a viscosity of 13,000 cs. at 65 F. is the maximum allowable to start an engine at this temperature. Most of the hindered polyol esters will not fall within these prescribed low temperature viscosity limits.

It has been discovered according to this invention that blends of certain hindered polyol esters provide gas turbine lubricants which have suitably functional viscosities at 65 F., e.g., 13,000 cs. or less, without sacrifice of the desired oxidation stability and corrosion resistance. This is an unexpected result, since the individual essential components of said blends do not possess functional vis-* cosities within the maximum limits prescribed above.

The particular blends of the esters found to be suitable are those having from about 30 to 60% of a neopentyl glycol ester of one or more monocarboxylic alkanoic acids having from 7 to 10 carbon atoms, and from about 40 to 70% of at least one other ester of the fully hindered polyol type selected from the group consisting of trimethylol ethane, trimethylol propane, trimethylol butane, pentaerythritol and mixtures thereof with one or more mono-carboxylic alkanoic acids having from 5 to 10 carbon atoms. The percentages are based on the total Weight of the blend of hindered polyol esters. When a pentaerythritol ester is used with the neopentyl glycol ester, carbon chain length of the esterifying acid is preferably from 5 to 10, while with the trimethylol alkane ester, the acid preferably has a chain length of 7 to 10 carbon atoms.

Other esters suitable for use in lubricant base fluids and recognized for such purpose may be used in minor quantities, e.g., up to 25% or more, as long as the advantages of the invention are preserved by utilizing the proportions of the fully hindered polyol ester specified above. For example, suitable esters which may be mentioned are 2,2,4 trimethylpentanediol dipelargonate, di-2 ethylhexyl azelate, diisodecyl adipate, diisooctyl sebacate, isodecyl pelargonate, diethylene glycol dipelargonate and mixtures of the same.

.The invention primarily overcomes the viscosity deficiencies of the otherwise desirable hindered esters. Specifically, diesters of neopentyl glycol prepared from monocarboxylic alkanoic acids containing from 7 to 10 carbon atoms when used alone cannot meet the viscosity limits set by the US. Specification MIL-L-7808F because they have pour points above F. Esters of trimethylol propane, and adjacent homologs prepared from alkanoic monobasic acids containing from 7 to 10 carbon atoms when used as the sole ester base fluid fail to meet specification MIL-L-7808F in that the 65 F. viscosity of these esters is Well in excess of the 13,000 cs. maximum required. The esters of pentaerythritol or dipentaerythritol or mixtures thereof, prepared from aliphatic monobasic acids containing from 5 to 10 carbon atoms again are unsuitable for application against Specification MIL- L-7808F by reason of excessive 65 F. viscosity.

It is remarkable, therefore, that by blending the abovementioned esters in Various essential proportions synthetic lubricant base fluids can be prepared which meet the low temperature viscosity requirements of MILL7808F. Table 1 provides an illustration of the drastic reduction in low temperature viscosity obtainable with the blended esters of this invention.

TABLE I.VISCOSITY MEASURED BY- Ester Viscosity Viscosity -65 F. 05. 210 F. cs.

(1) Neopeutyl glycol dipelargonate (Cm. 2. 6 (2) Trimethylol propane dipleargonate (Om, monoheotauoate (C1) 28. 000 4. 2 (3) Peutaerythritol tetravalerate (C5)4 25,000 3.35 (l) 55% TM? (CT)(C9)2,2 45% NPG (C02 9, 685 3. 36 (5) 55% TMP (O1)(C9)2, 45% NPG (CE) in 9, 760 3. 19 (6) 60% PE (004, 40% NPG (O7)(C9) 8, 350 3.0 PE 5) v)2, NPG 1) (C9) A. 11,500 3.15 PE ab, NPG (07x09),

20% 2,2,4-trimethyl pentanediol (C9)2---- 7, 625 2. 98

1 Freezes at 50 F.

2 TMPtrimcthyl0l propane.

3 NPG-neopentyl glycol (2,2 dimethyl propanediol). 4 PEpentaerythritol.

5 (i-O5)diisova1erate.

Compounded lubricants prepared from the blended hindered polyol esters of the invention have greater oxidationcorrosion stability than lubricants from blends of polyol esters with diesters of alkanedioic acids, e.g., azelaic acid with an alkanol. The latter blends are suggested in British Patent 927,794. This is illustrated by the data of Table II using blended esters of the following compositions and properties compounded with the additives designated.

Blend 1 60% pentaerythritol tetravalerate 1 40% neopentyl glycol dipelargonate Viscosity at 210 F.=:3.0 cs. Viscosity at 65 F: 8,350 cs. Acid value:0.06 Additives:

1.0% phenyl-a-naphthy*lamine 2 0.66% dioctyldiphenylamine 0.02% dihydroxyanthraquinone Blend 2 78.4% di-Z-ethylhexyl azelate 1 21.6% trimethylolpropane dipelargonate monoheptanoate Viscosity at 210 F.:3.'22 cs. Viscosity at 65 F.:8,206 cs. Acid value=0.06 Additives:

1.0% phenyl-u-nap-hthylamine 2 0.66% dioctyldiphenyl-amine 0.02% dihydroxyanthriquinone 1 Percentage by weight of ester blend. 2 Percentage by weight of base fluid.

3 Test procedure 100 ml. of the test lubricant were placed in a 50 mm. O.D. test tube. The 5 test metals, wired together, were placed in the test liquid. A water jacketed condenser and an air delivery tube were placed on the test tube. The apparatus was placed in a constant temperature heating block for 72 hours at 400 F.- 2 F. with air being delivered to the bottom of the test tube at a rate of 5 liters per hour during the test period. At the conclusion of the test the viscosity, acid value, and metal surface corrosion were measured and are recorded below in Table 11.

TABLE II OXIDATION-COEROSION, DEED-23699 (WEP) TEST RUN 72 HOURS AT 400 F.

This data clearly shows the hindered ester blends to be superior to the linear aliphatic diester-hindered ester blend in regard to viscosity degradation, acid formation and metal corrosion.

The polyol esters of the invention are preferably pre pared by esterification of the polyol and a slight excess of the alkanoic acid or mixed acids with or without a typical esterification catalyst, for example, paratoluene sulfonic acid, phosphoric acid, benzene sulfonic acid, and various metallic salts such as butyl titanate or dibutyl tin oxide, the catalyst being generally used in amounts between 0.02 and about 1% by weight of the reactants.

The esterification is conducted at temperatures preferably between about 150 and 240 C. for a period of 6 to 12 hours with the esterification water being removed continuously by vaporization, generally utilizing a liquid hydrocarbon, such as toluene, to form an azeotropic mixture to facilitate removal of the water.

After the water of reaction has reached the theoretical amount, the excess acid is removed by distillation. At this point the acid value of the reaction mixture usually does not exceed 5 mg. KOH per gram of sample. Thereafter, residual acid is neutralized and the catalyst is removed. The preparation of the ester, of course, does not form any part of the present invention.

In addition to base stock comprising the two essential fully hindered polyol esters, and any minor quantities of other esters as specified above, the base fluids are usually compounded into finished lubricants by addition of small quantities of additives, such as oxidation inhibitors, antiwear additives, extreme pressure agents, metal deactivators and defoamers.

Antioxidants 0.5 to 2.0% phenyl-a-naphthylamine, phenyl-b-naphthylamine, diphenylamine, dioctyl diphenylamine, phenothiozine, dioctyl phenothiozine, 2,2-dipyridal amine.

Metal deactivators 0.001 to 1.0% dihydroxy anthriquinone, di-t-butyl phenol, 2,4,6 tri-t-butyl phenol, disalicylal propylene diimine.

The following examples provide a complete specific embodiment of a method of preparation of the blended polyol esters of the invention.

EXAMPLE I 134 grams (1.0 mole) of pent-aerythritol and 510 grams (5.0 moles) of valeric acid were charged into a reaction vessel and heated to 210 C., removing the water of reaction as it formed by means of an azeotrope with xylene. Reacted 6 hours until the hydroxyl value was below 3.0. Stripped the excess Valerie acid and xylene under high vacuum to 234 C. cooled to room temperature and broke vacuum. Alkali refined using 50% excess 10% aqueous NaOH solution followed by distilled water washing until the Wash water was neutral to phenolphthalein. Vacuum dried to C./l mm. Hg. Final acid value was 0.04; hydroxyl value 0.0.

EXAMPLE II 102 grams (1.0 mole) of neopentyl glycol was reacted with 347 grams (2.2 moles) of pelargonic acid to 230 C. removing the water of reaction by means of a xylene azeotrope. Reacted 4 hours to a hydroxyl value below 3.0. Stripped the excess pelargonic acid and xylene under high vacuum to 230 C. Alkali refined the product using 50% excess of 10% NaOH solution followed by distilled water washes until the wash water was neutral to phenolphthalein. Vacuum dried the product to 90 C./l mm. Hg. Final acid value was 0.02; hydroxyl value 0.0.

EXAMPLE III 600 grams of pentaerythritol tetravalerate and 400 grams of neopentyl glycol dipelargonate were charged into a 2-liter beaker. The components were thoroughly mixed by agitating for /2 hour with a mechanical agitator. This resultant blend is the base ester for the following compounded lubricant.

989.5 grams of the above ester were charged into a beaker. 5.0 grams of phenyl-a-naphthylamine, 5.0 grams dioctyl diphenylamine and 0.5 gram dihydroxy anthraquinone were added to the ester and blended by heating to C. to C. with constant agitation for /2 hour. The final properties of the finished lubricant are listed below:

Kinematic viscosity at 210 F "cs-.. 3.0 Kinematic viscosity at 100 F. cs 11.8 Kinematic viscosity at -65 F cs 8350 Acid value 0.10 Flashpoint F 415 Pour point F 100 As used herein viscosity means kinematic viscosity measured in centistokes as prescribes in ASTM method D445-61. I

What We claim is:

1. A lubricant base fluid comprising a blend of fully esterified polyol esters having as essential constituents from 30 to 60% of a neopentyl glycol ester of at least one monocarboxylic alkanoic acid having from 7 to 10 carbon atoms and from about 40-70% of at least one other ester of a fully hindered polyol selected from the group consisting of pentaerythritol esters formed from monocarboxylic alkanoic acids having from S to 10 carbon atoms, trimethylol propane, trimethylol ethane, and trimethylol butane esters formed from monocarboxylic normal alkanoic acids having from 5 to 10 carbon atoms, said percentages being by weight of the total quantity of fully hindered polyol ester.

2. The lubricant base of claim 1 wherein said esters of trimethylolpropane, trimethyl ethane and trirnethylol butane are formed from normal monocarboxylic acids having from 7 to 10 carbon atoms.

3. A lubricant base fluid according to claim 1 in which the neopentyl glycol ester is the dipelargonate and the other fully hindered polyol ester is pentaerythritol tetravalerate.

4. A lubricant base fluid according to claim 1 in which the neopentyl glycol ester is the dipelargonate and the other fully hindered polyol ester is trimethylol-propane dipelargonate mono-n-heptanoate.

5. A lubricant base fluid according to claim 1 in which the other fully hindered polyol ester is a mixture of pentaerythritol tetravalerate and trimethylolpropane dipclargonate mono-n-heptanoate.

6. A lubricant suitable for gas turbine engines comprising a base fluid consisting essentially of about 40-45% of a fully esterified neopentyl glycol ester of at least one monocarboxylic alkauoic acid having from 7 to 10 carbon atoms and from about 5560% of at least one other fully esterified ester of a fully hindered polyol selected from the group consisting of pentaerythritol esters formed from monocarboxylic alkanoic acids having from 5 to carbon atoms, trimethylol propane, trimethylol ethane, and trimethylol butane esters formed from monocarboxylic normal alkanoic acids having from 5 to 10 carbon atoms, said percentages being by Weight of the total quantity of fully hindered polyol ester.

7. A lubricant according to claim 6 having about neopentyl glycol dipelargonate and about trimethylolpropane dipelargonate mono-n-heptanoate.

8. A lubricant according to claim 7 having about 40% neopentyl glycol monopelargonate mono-n-hept-anoate, and about pentaerythritol tetravalerate.

References Cited by the Examiner UNITED STATES PATENTS 1/1958 Hartley et 'al. 252-56 8/1962 Girard et al 260404.8

OTHER REFERENCES DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistan Examiner. 

1. A LUBRICANT BASE FLUID COMPRISING A BLEND OF FULLY ESTERIFIED POLYOL ESTERS HAVING AS ESSENTIAL CONSTITUENTS FROM 30 TO 60% OF A NEOPENTYL GLYCOL ESTER OF AT LEAST ONE MONOCARBOXYLIC ALKANOIC ACID HAVING FROM 7 TO 10 CARBON ATOMS AND FROM ABOUT 40-70% OF AT LEAST ONE OTHER ESTER OF A FULLY HINDERED POLYOL SELECTED FROM THE GROUP CONSISTING OF PENTAERYTHRIOL ESTERS FORMED FROM MONOCARBOXYLIC ALKANOIC ACIDS HAVING FROM 5 TO 10 CARBON ATOMS, TRIMETHYLOL PROPANE, TRIMETHTYLOL ETHANE, AND TRIMETHYLOL BUTANE ESTERS FORMED FROM MONOCARBOXYLIC NORMAL ALKANOIC ACIDS HAVING 5 TO 10 CARBON ATOMS, SAID PERCENTAGES BEING BY WEIGHT OF THE TOTAL QUANTITY OF FULLY HINDERED POLYOL ESTER. 